1. Field of the Invention
The present invention relates to a power semiconductor device, and more particularly, to a power semiconductor device capable of improving performance and the degree of integration of an integrated circuit and realizing integration between a switching element and the integrated circuit without deteriorating a heat radiation characteristic.
2. Background Art
To control the operation of a motor, it is necessary to change the amount and the direction of electric current which flows through a coil provided inside the motor. A switching element is used to control electric current which flows through such an inductive load. The switching element turns ON/OFF between first and second main electrodes in response to a control signal inputted to a control electrode. A control circuit controls ON/OFF of the switching element by giving a voltage or an electric current signal to the control electrode of the switching element. A bridge circuit or the like is constructed by combining a plurality of such switching elements.
When an electric current equal to or above a predetermined value flows through the switching element or when a voltage equal to or above a predetermined value is applied between the first and second main electrodes, power loss or dielectric breakdown of a semiconductor junction or the like thereby caused may lead to fatal destruction. This may prevent normal driving of the motor or the like. To avoid this, the control circuit is provided with a protection function for preventing destruction of the switching element (e.g., see Japanese Patent Laid-Open No. 2004-96318).
Realizing the protection function of the switching element requires a circuit which detects the condition of the switching element and a circuit which processes a detected signal. The control circuit is generally arranged in a concentrated manner at a certain distance from locations where a plurality of switching elements are mounted. On the other hand, the circuit which protects the switching element is preferably installed in the vicinity of the switching element.
As shown in FIG. 28, a switching element provided with a protection function is in actual use in recent years in which a switching element section 201 and a circuit element 202 for protecting the switching element are configured within the same substrate. Manufacturing this power semiconductor device requires a process of forming the circuit element 202 in addition to a process of forming the switching element section 201. However, the process of forming the switching element section is unnecessary for the circuit element 202, while the process of forming the circuit element is unnecessary for the switching element section 201. Therefore, commonality between both processes is generally sought after and as the degree of commonality increases, the number of useless processes decreases. However, there may be cases where manufacturing conditions such as most desirable concentration of impurities or depth of diffusion cannot help being changed in achieving commonality. Therefore, the higher the rate of commonality, the greater is the sacrifice in the aspect of performance.
However, in the case of an apparatus in which only a small amount of current is driven by the switching element, the whole product needs to be downsized, and this is likely to cancel out an increase of the manufacturing cost caused by the above described useless processes. On the other hand, in the case of an apparatus in which a large amount of current is driven by the switching element, the problem of power loss when the witching element is ON is considerable, and therefore there is a strong tendency to give priority to the performance of the switching element.
Furthermore, to reduce power loss of the switching element, it is effective to increase the size of the switching element and thereby reduce electric resistance. However, when forming a small circuit element in a large switching element, the waste in the process of forming the circuit element increases for the switching element, the manufacturing cost of the whole apparatus increases and the merit in incorporating the circuit element in the switching element fades away.
Therefore, as shown in FIG. 29, a power semiconductor device is in practical use in which an integrated circuit element 204 for protecting a switching element 203 is bonded onto the surface of the switching element 203 on a chip-on-chip basis and both are wire-bonded together. In this way, configuring the switching element 203 and the integrated circuit element 204 as separate chips prevents the process of forming the integrated circuit element 204 from being affected by the process of forming the switching element 203 and the processes can be optimized with an emphasis placed on improvements of the performance and the degree of integration of the integrated circuit.